1. Field of the Invention
The present invention relates to a key switch assembly for a computer keyboard, more particularly to a key switch assembly which has a relatively simple and stable structure with a reduced thickness.
2. Description of the Related Art
In U.S. patent application Ser. No. 09/031,414, now U.S. Pat. No. 5,878,872, the Applicant disclosed a key switch assembly which includes a base board, a membrane circuit layer, a resilient layer, a scissors-type key cap support, and a key cap. The base board is formed with a pair of upwardly projecting slide retainer plates, a pair of upwardly projecting pivot retainer plates, and a stop projection. Each of the slide retainer plates has a vertical portion and a lateral horizontal portion on a top end of the vertical portion. The membrane circuit layer and the resilient layer are superimposed in sequence on the base board, and are formed with aligned openings to permit extension of the slide retainer plates, the pivot retainer plates and the stop projection therethrough. The resilient layer is provided with an upright resilient member. The key cap support includes first and second support levers. The first support lever has a lower portion which is retained pivotally by the pivot retainer plates of the base board, and an upper portion which is retained slidably by a slide retainer unit of the key cap. The second support lever has a lower portion formed with a pair of outward slide shafts which are retained slidably by the slide retainer plates of the base board, and a pair of inward slide shafts, and an upper portion which is retained pivotally by a pivot retainer unit of the key cap. The inward slide shafts extend through the openings formed in the resilient layer and press against the membrane circuit layer. The key cap is biased upwardly by the resilient member.
It is found that the slide shafts on the lower portion of the second support lever are retained on the base board merely by virtue of the lateral horizontal portions of the pair of spaced-apart slide retainer plates of the base board. Thus, the engagement between the key cap support and the base board is not stable enough.